Asphalt pavements include asphalt binders combined with aggregates compacted to a known and/or desired density. Asphalt binders have been described to function as a water-resistant thermoplastic adhesive that “glues” the aggregates together. The asphalt binder is commonly a residue from petroleum refining chosen from certain crude oil blends processed to have suitable endurance and other functional properties. Additives (such as polymers) can be blended or reacted with the binder (to modify binder properties and enhance performance as is well known to those of skill in the art). See Anderson et al., Asphalt Binders, A2D01: Committee on Characteristics of Bituminous Materials, at URL,
nas.edu/gulliver.trb/publications/millennium/00006.pdf.
Asphalt binders (as well as the selection of aggregates) can be customized for each site or project. The asphalt binders may be selected for a particular application, expected climate of operation/use, established maximum and minimum temperatures within a cycle, and/or other desired characteristics when designing a pavement mixture. Asphalt binders may be graded under the PG (performance graded) binder specification standard developed by the Strategic Highway Research Program (SHRP). In this grading system, the first two digits of the binder identifier can present an average 7-day maximum pavement design temperature and the last two digits can reflect an average 7-day minimum pavement design temperature. Thus, for example, a binder identified as PG 64-22 binder reflects an average 7-day maximum temperature of 64° C. and an average 7-day minimum of 22° C. The temperatures can be established using the SUPERPAVE (an acronym for “SUperior PERforming ashpalt PAVEments”) weather database, which includes over 5,000 weather stations across the United States. The pavement temperatures can be calculated using air temperatures measured at the weather stations using well-known models.
Most paved roads in the United States are surface-paved with hot-mix formulations of asphalt containing generally about at least 93–96% aggregate and 4–7% asphalt binder (and typically including some number of air voids after compaction, such as between about 3–10%).
Stripping is a phenomenon of the loss of the bond between asphalt binder and the aggregate resulting in physical separation and degradation of the pavement. One of the common causes of stripping is the presence of water or moisture on and/or in the pavement. The potential for stripping due to moisture can be reduced by using anti-stripping additives in asphalt mixtures or asphalt binders. Examples of anti-stripping additives are hydrated lime, cement, polymer based and/or other liquid chemicals. Anti-stripping agents can be added in lesser amounts than either the aggregates or asphalt binder, such as between about 0.1–3%, and typically about 0.5–2% percent, of the total asphalt binder weight. For example, when hydrated lime is used, between about 1–2% of anti-stripping agents are used as compared to between about 0.5–1.0% for when other liquid chemicals are used, of the total asphalt binder weight.
In the past, the anti-stripping additives in the mixture could be indirectly evaluated through the performance of the asphalt pavement, such as by using standard test method AASHTO T283. Unfortunately, this method generally takes several days to obtain results. This delay and/or inconvenience may limit the number of inspections performed to verify the presence or level of anti-stripping agents in the asphalt mixtures. In addition, the potential variability in the dosage of anti-stripping additives employed, batch to batch, can introduce uncertainties in the quality of the paved roadway and may cause or contribute to premature degradation of the roadway surface.
In view of the above, there remains a need to provide economical methods and devices that can assess the presence and/or level of anti-stripping agents in asphalt related materials. There is also a need to provide anti-stripping agent tests that can be readily obtained and completed in reduced time so as to provide prompt reporting of the test results to facilitate increased numbers of inspection opportunities and/or increased control of the content of anti-stripping agents in asphalt binders or asphalt mixtures when delivered to construction sites.